Do i have to update my ipad mini?

No nobody is forcing you to update it your choice

If it's an iPad mini 1st gen, you may be better off staying at the iOS version you are at now (7.1.1). If you are not running (or plan to run) apps that require iOS 8 or above, I would personally keep the iPad's iOS where it is. There have been complaints from those who've updated to iOS 8 with bad results, performance-wise that sometimes need a full device restore (as new) to resolve. OTOH, many have no issues after the update. The iPad 2 and the mini 1st gen are pretty much the same device (camera differences and Bluetooth chipset being the main differences) so they would likely have the same performance issues (if they do materialize). This is the reason I would stay at your current iOS version...you don't know IF you'll have issues and if you do, realize that you cannot revert/backdate the iOS so you'll need to use other means to resolve any issues.

In the end, the decision is up to you...good luck making it.

if you are love to explorer new features of iOS then should be update because apple always try to improve features and fix bugs in new version so lets check out new version of iOS. make sure you are fully decided that because you can't go revert back to current version if update once